In German Patent Application No. DE 40 32 927, a device is described for improving visibility conditions in a motor vehicle. Here, the image acquired by an infrared-sensitive camera is visually superposed with a display device, formed as a head-up display, as a virtual image of the exterior landscape, and is displayed to the driver. In addition, at least one source of radiation having an infrared portion is provided for the irradiation of the area perceived visually by the driver in the direction of travel.
Such night vision systems (night view, or NV systems), as described in German Patent Application No. DE 40 32 927, based on light having wavelengths in the near-infrared (NIR) wavelength range, illuminate the area in front of a motor vehicle using infrared headlamps (near-infrared headlamps, or NIR headlamps), in general having a high-beam characteristic. Under certain conditions, the NIR radiation, which is invisible for human beings and most animals, can harm the eyes of humans and animals situated within the range of action of such an NIR headlamp. In order to avoid such damage, it is conceivable to calculate minimum distances for particular radiation strengths between NIR headlamps and the eye that must not be undershot, and that can for example be ensured through constructive measures.
Besides constructive measures, from German Patent Application No. DE 101 26 492 an alternative method is described to prevent damage to traffic participants by NIR light. A method is provided in which laser light having a wavelength outside the visible spectrum is radiated only if the motor vehicle is in motion. Furthermore, it is known to activate NIR in headlamps beginning only at a certain minimum speed, for example 30 km/h. A disadvantage of this method is that the night vision function of a night vision system is not available when the motor vehicle is at a standstill and/or is traveling slowly, although here as well situations can occur in which the night vision function would be useful. For example, a night vision function would be useful when traveling slowly on off-road paths or on narrow side streets. Furthermore, frequent switching on and off of the NIR headlamps has an adverse effect on their life span. In particular in a stop-and-go situation, and/or traffic situations in the vicinity of the minimum speed, a high degree of strain is placed on the NIR headlamps. This can have the result that the user acceptance of such a night vision system is reduced due to this limited availability.
In the above-cited German Patent Application Nos. DE 40 32 927 and DE 101 26 492, no indications are found of a damage-free method for improving visibility in a motor vehicle that simultaneously operates with a high degree of availability.